Hybrid-electric and pure electric vehicles rely on a traction battery to provide power for propulsion. As the power stored in a traction battery is not endless, properties of the traction battery must be monitored to track the present capability of the traction battery. One important quantity is the battery power capability which indicates how much power the battery may supply or absorb at a given time. Another important quantity is the battery state of charge which indicates the amount of charge stored in the battery. There are many known schemes for estimating these quantities.
A traction battery system will generally measure voltages and currents associated with the traction battery. In an ideal world, the sensors used to measure these voltages and currents would provide accurate information. Unfortunately, the environment in an automobile may be an electrically noisy environment. The sensors generally experience some measurement biases. The battery pack is constructed of many battery cells. Physical battery properties, such as current, voltage and temperature, may be measured by different sensors at different sample rates. Asynchronization issues may arise as the sensors may be sampled sequentially and filtered differently. The biased signals are then used for calculations leading to inaccurate values. These inaccurate values and asynchronization phenomenon may lead to incorrect estimation of battery parameters.
Prior art techniques of compensating for measurement biases include measuring the sensors when no load is applied. The value measured during the no-load condition is then added or subtracted to the measured values during operation to yield a corrected sensor value. This approach requires that there be some predictable no-load operation intervals. For a traction battery system, the no-load measurement may be performed before closing a main contactor that connects the traction battery to an electrical load. This may cause delays in closing the main contactor and inaccurate measurement biases. This method also cannot compensate for changing biases during extended operation periods.